Currently, the most ubiquitous cellular communication system is the 2nd generation communication system known as the Global System for Mobile communication (GSM). Further description of the GSM TDMA communication system can be found in ‘The GSM System for Mobile Communications’ by Michel Mouly and Marie Bernadette Pautet, Bay Foreign Language Books, 1992, ISBN 2950719007.
To further enhance the services and performance of the GSM communication system, a number of enhancements and additions have been introduced to the GSM communication system over the years.
One such enhancement is the General Packet Radio System (GPRS), which is a system developed for enabling packet data based communication in a GSM communication system. Thus, the GPRS system is compatible with the GSM (voice) system and provides a number of additional services including provision of packet data communication, which augments and complements the circuit switched communication of a traditional communication system. Furthermore, the packet based data communication may also support packet based speech services. The GPRS system has been standardised as an add-on to an existing GSM communication system, and can be introduced to an existing GSM communication system by introducing new network elements. Specifically, a number of Serving GPRS Support Nodes (SGSN) and Gateway GPRS Support Nodes (GGSN) may be introduced to provide a packet based fixed network communication.
3rd generation systems are currently being rolled out to further enhance the communication services provided to mobile users. One such system is the Universal Mobile Telecommunication System (UMTS), which is currently being deployed. Further description of CDMA and specifically of the Wideband CDMA (WCDMA) mode of UMTS can be found in ‘WCDMA for UMTS’, Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876. The core network of UMTS is built on the use of SGSNs and GGSNs thereby providing commonality with GPRS.
3rd Generation cellular communication systems have been specified to provide a large number of different services including efficient packet data services. For example, downlink packet data services are supported within the 3rd Generation Partnership Project (3GPP) release 5 Technical Specifications in the form of the High Speed Downlink Packet Access (HSDPA) service.
In accordance with the 3GPP specifications, the HSDPA service may be used in both Frequency Division Duplex (FDD) mode and Time Division Duplex (TDD) mode.
In HSDPA, transmission code resources are shared amongst users according to their traffic needs. The base station (also known as the Node-B for UMTS) is responsible for allocating and distributing the HSDPA resources amongst the individual calls. In a UMTS system that supports HSDPA, some of the code allocation is performed by the RNC whereas other code allocation, or more specifically, scheduling is performed by the base station. Specifically, the RNC allocates a set of resources to each base station, which the base station can use exclusively for high speed packet services. The RNC furthermore controls the flow of data to and from the base stations. However, the base station is responsible for scheduling HS-DSCH transmissions to the mobile stations that are attached to it, for operating a retransmission scheme on the HS-DSCH channels, for controlling the coding and modulation for HS-DSCH transmissions to the mobile stations and for transmitting data packets to the mobile stations.
HSDPA seeks to provide packet access techniques with a relatively low resource usage and with low latency.
Specifically, HSDPA uses a number of techniques in order to reduce the resource required to communicate data and to increase the capacity of the communication system. These techniques include Adaptive Coding and Modulation (ACM), retransmission with soft combining and fast scheduling performed at the base station.
However, in communication systems which support a number of different services, it is critical that the system can be flexibly optimised for different scenarios. For example, as the different service types all make use of the limited air interface resource, it is important that the available resource is effectively shared by the different types of communication services.
Specifically, in UMTS communication systems HSDPA services and conventional UMTS services as defined in Release 99 (R99) of the UMTS technical specifications typically share the same interference or power resource. In addition, the spreading of signals is based on spreading codes which are selected to achieve orthogonality in the downlink direction. In order to ensure that this orthogonality is maintained between different service types, the R99 and HSDPA services share the same code tree of orthogonal spreading codes (known as Orthogonal Variable Spreading Factor—OVSF codes).
The allocation of resource to a specific service type can impact the Quality of Service offered by that service and/or the capacity of that service. For example, if all the available resource for a communication service type is fully exploited, some communications may be dropped and/or new communications are prevented from being initiated.
A solution that is typically used to solve this problem is to allocate a fixed proportion of the resource to each service, i.e. the resource is not dynamically shared but is dedicated to one specific service in accordance with a resource partitioning. However, this tends to result in inefficient resource usage and reduced performance and capacity as the resource allocation tends not to reflect the varying conditions or requirements. For example, it can frequently occur that e.g. R99 services require more than the allocated resource allocation whereas the HSDPA services do not use the resource available to them.
Hence, an improved system resource allocation in a cellular communication system would be advantageous.